Many handheld computing devices allow users to input information by making direct contact with the display surfaces of the devices using either fingers (i.e., “touch input” or “touch-based input”) or stylus-type input devices. Some computing devices furthermore permit use of distinct or tagged physical objects, including pucks, specialized tools such as brushes or airbrushes, mobile devices, toys, and other physical icons or tangible props. These types of input mechanisms are collectively referred to herein as contact-type input mechanisms.
For example, typical touch-based input mechanisms generally respond to direct touch inputs when a user touches a display surface of the computing device with one or more fingers. Similarly, typical pen- or stylus-based input mechanisms respond to direct pen or stylus input events when a user contacts the display surface with a pen or stylus device.
Unfortunately, both of these types of interface mechanisms introduce a number of challenges. For instance, consider the case in which a computing device allows a user to input information using both a touch input mechanism and a pen input mechanism. In the course of applying a mark on the display surface with a pen device, the user may inadvertently rest his or her palm (or other portion of the hand or wrist) on the display surface. The computing device may then incorrectly interpret this inadvertent palm contact as legitimate input activity, thereby causing potentially unwanted behavior by the computing device. A similar challenge may confront a user who is intentionally using the touch input mechanism. The user may attempt to apply a focused touch to a target object presented on the display surface, yet the user may accidently brush or bump his or her hand (or a pen or stylus device held in that same hand) against other parts of the display surface, causing accidental input events. Workflow disruptions to the user resulting from such problems may understandably frustrate the user whenever they occur.